How would a straight man be expected to react to the startling discovery that the woman he had been having sex with was actually a biological male?

He might be nonplussed. He might feel shock and anger at the deception. Or might he experience an enraging surge of what's sometimes called "gay panic" -- perhaps in a wave potent enough to drive him to batter the individual senseless with fists and a skillet, strangle her, and then bury her body in a shallow grave in the El Dorado National Forest?

So goes a line of defense being advanced on behalf of two East Bay men charged with just such a crime against 17-year old Gwen Araujo, who was born Eddie but had identified as a female since puberty. Later this week, a jury may be asked to render its verdict in the closely watched trial, which is the latest in which defendants hope jurors will subconsciously recoil from the idea of gay sex and sympathize with the defendants' violent reaction.

Although the tactic was once reliable to persuade juries to be more lenient toward defendants who killed gay or transgender victims, a review of recent cases suggests it's now a tougher sell. One reason may be that experts say such killings of gays tend to be particularly gruesome compared with hate crimes against other groups, undercutting jurors' sympathies.

The term "gay panic" had its origins in decades-old research suggesting that certain men are terrified by their own latent homosexual tendencies -- prompting the theory that a gay advance might yank all those emotions out into the open and trigger an aggressive, even murderous, response. Several men convicted of gay bashing said they had previously been molested by a man or suffered guilt over participating in consensual gay sex.

But "gay panic" has developed a rather elastic definition, with some defense attorneys using it as catch-all characterization of a straight man's revulsion at being on the receiving end of a gay man's pass. Activists retort that if women were permitted the same leeway to violence when faced with unwelcome sexual advances, the world would have far fewer heterosexual men.

The Araujo case, of course, ups the ante: Instead of a sexual proposition, what transpired was actual sex. And the victim wasn't gay but transgender -- something more exotic to a typical suburban jury.

Defense attorneys tried unsuccessfully at a preliminary hearing to get charges scaled back from murder to manslaughter in the killing of Araujo. Alameda County prosecutors have asked the jury to convict Fremont resident Michael Magidson and Newark resident Jose Merel, who according to testimony had sexual relations with Araujo, of first-degree murder with a hate-crime enhancement, which could earn them 25 years to life. Their friend Jason Cazares is also charged with her murder, although his lawyers said that, at most, he helped bury her out of loyalty to his friends.

Co-defendant Jaron Nabors pleaded guilty to voluntary manslaughter and will be sentenced to 11 years in prison in exchange for his testimony. He told the jury his friends became suspicious about Araujo's gender in September, noting that her voice was scratchy and that during sex she had never allowed them to touch her genitals. On the night of Oct. 4, 2002, they forced the issue and learned the biological reality that sent Merel into a sobbing mantra: "I can't be . . . gay."

An acquaintance, Nicole Brown, testified that she tried to comfort Merel. "I put my hands on his shoulder and said 'This is not your fault. You were a football player.' "

The brutal attack that followed inside the Newark home amounted to "manslaughter in the heat of passion," Magidson's attorney Michael Thorman told the jury. He contended that Magidson's discovery that he had unknowingly engaged in homosexual sex ignited revulsion and rage.

Prosecutors contend there was premeditation in the men's actions. "They decided," said Deputy District Attorney Chris Lamiero, "that the wages of Eddie Araujo's sin of deception were death."

Araujo's family hopes for a verdict far different than the one delivered seven years ago by a Boston jury against computer programmer William Palmer. He claimed he picked up Chanelle Pickett in a bar without realizing she was biologically male. The medical examiner testified that Pickett was beaten and "throttled" for eight minutes, but the jury acquitted Palmer of murder and manslaughter, convicting him merely of assault and battery. Decrying Pickett's two-year sentence, transgender observer Toni Black said "I've seen people get more jail time for abusing animals. ... We've been judged expendable."

In 1995, Jonathan Schmitz reported being "humiliated" when friend Scott Amedure revealed during a taping of "The Jenny Jones Show" that he had a secret crush on him and fantasized about covering him with whipped cream and strawberries. Three days later he bought a shotgun, drove to Amedure's trailer and shot him twice through the heart. Juries in two trials reached the same verdict: guilty of murder, but only in the second degree.

In 1999, former skinhead Steven Mullins invoked a "gay panic" defense in the slaying of textile worker Billy Jack Gaither, who he said had propositioned him. Mullins said he and a co-defendant enticed Gaither with the promise of a sexual threesome before beating him with an ax handle and setting him on fire atop kerosene-soaked tires. The Alabama jury didn't buy "gay panic" as a mitigating factor: It convicted both men of capital murder. They were sentenced to life in prison without possibility of parole.

As for Araujo's killers, "This crime didn't occur because Mike had a bias. It happened because of the discovery of what Eddie had done," said Magidson's attorney, Thorman. "This is a case that tells a story about ... the tragic results when that deception and betrayal were discovered."

Of course, deception is hardly foreign to heterosexual sex -- a 15-year- old girl might lie about her age to an older man, or a man may seduce a woman by posing as a photographer for Playboy. "Such deceits happen on occasion, but a jury probably would be unlikely to accept them as excuses for cold-blooded murder," said Cynthia Lee, a professor at George Washington University Law School and author of "Murder & the Reasonable Man." On the other hand, she noted, jurors are less likely to personally know someone who is transgender --

and "it's precisely that lack of familiarity could work in favor of a so- called gay panic defense."